Forgive Alf Clausen if he appears a bit tired. As musical director on Fox's long-running animated phenomenon "The Simpsons," Clausen was on hand this summer when the show reached the estimable milestone of Take 23,000. Overseeing those takes since Season 2, Clausen, who still puts in 80-hour weeks to come up with the show's music, is something of a pioneer in a genre that steadily has become an unexpected hotbed of musical experimentation.

"With animated shows in general, and with 'The Simpsons' in particular, reality gets suspended on a daily basis," he says. "Because of that, the musical palette you work with becomes much wider. Every time I think we've explored every possible music style there is, I'll go into a spotting session, and there'll be a request for a style we've never done before -- and all I can say is: 'D'oh! I forgot about that one.'"

Music for cartoons is no longer kids' stuff. From the tropically tinged cues that support the misadventures of Nickelodeon's "SpongeBob SquarePants" to the quirky sounds of Adult Swim and the orchestral sweep of underscore behind that yellow family from Springfield, some of the most interesting and accomplished music on television can be found in the soundtracks to animated programs.

Animated shows tend to use much more music per minute than do their live-action counterparts, and while a live sitcom, drama or reality program might use its music as a unifying signature element, animation can offer tremendous range and freedom for musical exploration. On some of the best animated shows, creators and composers regularly take advantage of that freedom, making use of perfectly tailored scores, original songs and savvy licensing opportunities.

"Simpsons" set the standard when it debuted 18 years ago, and its influence is evident in similarly cutting-edge animated fare such as Fox's "American Dad," "Family Guy" and "King of the Hill," which are among the few programs of any genre on which full acoustic orchestras play the scores for every episode. Clausen notes that in the case of "Simpsons," the live music reflects the vision and support of show creator Matt Groening.

"Matt and the producers don't view live music as an indulgence but as a very crucial way of supporting the animation," Clausen says. "Because of the grueling turnaround times, the animation can sometimes come back a little rougher visually than everyone would like, and Matt believes the acoustic music actually helps smooth it out."

While "Dad" and "Guy" consistently push boundaries in terms of content, composer Walter Murphy, who shares the musical workload on both programs with Ron Jones, says that composing for today's TV animation is a process similar to classic film work.

"We actually score in a way that's a throwback to more-traditional film scoring," he says. "The deadlines are tighter, but you're really scoring to picture and using music to help tell the story and to feel the emotions the characters are going through. At the same time, we're creating real production numbers and coming up with original songs, just like in the old musicals."

Unlike most TV programs, which rely on seasoned music supervisors to provide a hip, "of the moment" edge, animated programs use music that is often constructed to be trend-proof. It's doubtful that any amount of audience research would have indicated that kids would go crazy for a show featuring a sponge, a starfish and ukulele music, but the success of "SpongeBob" points up another example of creative vision matched with unusual and wide-ranging musical choices.

The show's score is pieced together each week by music editor Nick Carr, who culls appropriate cues from several large production music libraries. He also draws from an in-house library of "SpongeBob" music assembled with creator Steve Hillenburg, and, when the libraries can't cover all the show's undersea needs, Carr will do some spot composing.

"There are a lot of times when we want some silliness in the music, but there are also a lot of times where you play the emotions straight," he says. "If SpongeBob is worried about something, you want to really feel that."

But while many shows blaze their own trail, the animated genre is diverse enough to include what's genuinely hot in the music world. Cartoon Network's "Class of 3000," set to debut in November, is created and executive produced by Andre Benjamin of the rap duo OutKast. Benjamin will voice the lead character and contribute original songs for every episode.

In another stark difference to live-action television, original songs and lavish musical numbers have become a staple of many animated shows. On Nickelodeon's "The Fairly OddParents," creator Butch Hartman says that while songs weren't a part of his original vision, they became more of a regular feature once he discovered how effective they can be as a storytelling device.

"I'm a big Monkees fan, and as we moved along, we saw how much fun it would be to work songs in," he says. "The challenge is always in timing: You've only got 11 minutes to tell a story, and a song takes two minutes, so you've got to make sure the song moves the story along."

Hartman's songs, co-written with composer Guy Moon, also are featured on his other Nick show, "Danny Phantom," and some of those tunes have become hits in their own right.

"Through the show's Web site, there has been some demand for downloadable versions of the songs," Hartman says, adding that he takes it as a huge compliment when "kids actually want the stuff on their iPods."

Even if members of a show's audience can't tie their own shoes, let alone work an iPod, there is no reason to skimp on musical quality, according to Evan Lurie, a longtime fixture of New York's avant-jazz scene and the composer on Nick Jr.'s toddler-targeted "The Backyardigans." The show highlights a particular genre of music in each episode, requiring Lurie to write in the styles of disco, '80s pop, reggae, Western swing, Django Reinhart and Rossini, among many others.

"I don't really think of what I do as writing for kids," Lurie says. "It's more a matter of writing in these genres, for specific characters. I did one hip-hop episode where I spent about an hour trying to get the phrasing of a trumpet part just right. At one point, I did think: 'This is for 3-year-olds. Are they watching the show for the trumpet phrases?' You laugh, but you still put in the work to do it right. I don't cut any corners in terms of writing or recording this music."

At the other end of the animation audience spectrum are fans of Adult Swim, which is comprised of both absurdist comedies ("Aqua Teen Hunger Force," "Robot Chicken") and action-adventure anime ("Fullmetal Alchemist," "InuYasha"). The music in the shows reflects the diverse tastes of show creators, but Swim also has made an effort to help organically integrate talents from the pop music world both into the programs themselves and into the distinctive bumps between shows.

Hip-hop artist Schooly D kicks out the theme song for "Hunger Force," and the bumps feature a mix of cues drawn from the Turner library and music licensed from indie and underground acts. (A CD released last year -- Danger Doom's "The Mouse and the Mask" -- blends the talents of MF Doom and Danger Mouse and features cameos by various Adult Swim characters.)

The anime shows that Adult Swim features are licensed outright by the network, which does not alter the music that comes with them. Such shows typically feature a theme song by a Japanese pop band and a traditional, orchestral underscore done by a Japanese composer.

"Budget is always a big factor for us," Adult Swim head of music Jason DeMarco says. "Sometimes, you can't bring in an artist you might want for something because you just can't afford it, but sometimes it's worth reaching out because you find out that somebody's a fan of what we're doing and is willing to work with us."

One of Adult Swim's newest shows, "Metalocalypse," is another example of an animated program offering the freedom and unorthodox creative environment that most likely would never exist on a live-action show. Co-created by Brendon Small and Tommy Blacha, "Metalocalypse" follows the destructive exploits of the world's biggest band, Dethklok, which happens to play a ferociously aggressive style of death metal. The music is created nearly single-handedly by Small, a Berklee School of Music graduate who also composed for his previous Adult Swim creation, "Home Movies."

In lieu of a treatment or pilot script, "Metalocalypse" was pitched to Adult Swim with a theme song that Blacha and Small felt said everything that needed to be said about the show -- and Small has been shredding away on his guitar since the show was picked up.

"By default, I have a lot of freedom with the music," he says. "This is what the show's going to sound like because this is what I can do in this amount of time. We don't have a big-enough budget not to have that kind of freedom."

But "Metalocalypse" is not skimping on attention to musical detail: Small has secured endorsement deals with Gibson guitars, Krank amplifiers, Digidesign studio equipment and Line 6 effects pedals, all of which are featured in the show -- drawn accurately to Small's specifications. He also took his art staff to death-metal concerts so they could capture precisely the details of posture, hair-tossing and rock 'n' roll stage movements. Small even films himself as he plays guitar solos to be used in the show's score, giving its animators a reference point.

"The show's tone is very over-the-top, Monty Python-style comedy, but I wanted to get all the musical details right," Small says. "Overall, I think it has come together really well, and in terms of the music, given the fact that I get to crank up my guitar for every episode, the fat 15-year-old inside of me is extremely happy right now."

Such dedication might be de rigueur on a $1 million film project or a primetime drama, but on a half-hour animated show on cable? Clausen argues that while animation might not be afforded the same respect as other genres, there is no reason to take its music less seriously.

"The level of ('Simpsons') is so high to begin with -- nobody slacks off," he says. "Every week is different: I go from something that sounds like Steely Dan to something that sounds like Bernard Herrmann and from jazz to Mozart. You can't do that on any other kind of show. That's the best part of the job, and the part that keeps me awake."